First Scratch-Built

The Rocketry Forum

Help Support The Rocketry Forum:

sponge008

Member
Joined
Jun 19, 2004
Messages
14
Reaction score
0
So, I'm about to undertake my first scratch-built project. However, I'd like to check the parts list with you guys.
3 18" BT-50s
2 BT-50 tube couplers
2 1/8" launch lugs
1 PNC-50 nose cone
Some 3/32" balsa
BT-50 18mm engine mount kit (for A/B/C)

Now, the questions: Did I forget anything? Should I use a 12" or 18" chute? And finally, would a C engine be big enough for this? Thanks, guys. :D
 

saunassa

Active Member
Joined
Mar 11, 2004
Messages
37
Reaction score
0
are the 3 body tubes to be connected together for a total of 54"?

if they are to be connected together then i would use 2 3/16" launch lugs and would think about using a D-motor mount and then making an adapter for A-C motors.
 

DynaSoar

Well-Known Member
Joined
Mar 15, 2004
Messages
3,022
Reaction score
0
Originally posted by sponge008
So, I'm about to undertake my first scratch-built project. However, I'd like to check the parts list with you guys.
3 18" BT-50s
2 BT-50 tube couplers
2 1/8" launch lugs
1 PNC-50 nose cone
Some 3/32" balsa
BT-50 18mm engine mount kit (for A/B/C)

Now, the questions: Did I forget anything? Should I use a 12" or 18" chute? And finally, would a C engine be big enough for this? Thanks, guys. :D
3 tubes and 2 couplers, it's going to be a long 24mm minimum diameter bird, right? I don't think you'll be impressed with a C engine flight.

I'd scrap the 18mm mount and use the rings as thrust rings/engine blocks set at 3.5" up the tube. Then you could use E engines, or if you cut a 1" spacer from a spent C11, D12 or E9 (or a piece of coupler tube), you could fly it with C11s or D12s. You can even get an E size engine hook and use it even though it'd be on the outside of the rocket. Just glue a patch of some sort over the place where it goes through the body tube, for an anchor. If you do this, change the lugs to 3/16".

How much chute depends on how high you send it, and what sort of fins. If they're swept like an Alpha's, best to use a bigger chute and bring it down soft. If they're set above the tail a bit and/or not swept, like a Nike booster or WAC Corporal, they're a lot less likely to break and you can use a smaller chute.

If you do and you send it it, expect it to drift. A good choice might be to use an 18" but cut out right angle sections so it's an X-form chute (like a plus sign). They have about 90% of the area of the original, but a lot less drift.

Also, a bigger chute is more likely to be a problem if you send it high/faster unless you're real careful to select the right delay. If the ejection is too early or late, it's going real fast, and a larger chute will pop harder and be more likely to tear or lose shrouds.

Chutes are cheap, and easy to scratch build. Use a snap swivel on each and you can have more than one and swap them as you need to be higher flights, more wind, etc.
 

Fore Check

Well-Known Member
Joined
Sep 24, 2010
Messages
4,263
Reaction score
7
I disagree with the assessment that your rocket will be underpowered on 18mm power.

The Estes Cobra 1500 is designed almost the same way - 3 x 18" long body tubes with an 18mm engine mount. It will make 750' or so. The only difference is that the C1500 is based on a BT55 rather than a BT50.

Your design being based on a smaller diameter tube should fly higher, all else being equal.
 

vjp

Well-Known Member
Joined
Jan 23, 2009
Messages
1,487
Reaction score
0
sponge -

I "built" and flew your rocket in rocksim, and it should perform nicely on a C6-5, or a B6-4. The A8-3 performance is somewhat lackluster, I wouldn't attempt it myself. Here's a screen shot with the sim results.
 

vjp

Well-Known Member
Joined
Jan 23, 2009
Messages
1,487
Reaction score
0
Here's a copy of the RockSim file, if anyone wants it.
 

sponge008

Member
Joined
Jun 19, 2004
Messages
14
Reaction score
0
So, I guess that other than forgetting the shock cord, :eek: the rocket is good? I'm probably going to use high-set fins (like, a few millimeters above the bottom), so I guess a 12" chute will do, right? Thanks for the incredible amount of replies!

PS-will a 12" chute drift more or less than a "cut" 18"?
 
Top